7,775 research outputs found
Gaussianity revisited: Exploring the Kibble-Zurek mechanism with superconducting rings
In this paper we use spontaneous flux production in annular superconductors
to shed light on the Kibble-Zurek scenario. In particular, we examine the
effects of finite size and external fields, neither of which is directly
amenable to the KZ analysis. Supported by 1D and 3D simulations, the properties
of a superconducting ring are seen to be well represented by analytic Gaussian
approximations which encode the KZ scales indirectly. Experimental results for
annuli in the presence of external fields corroborate these findings.Comment: 20 pages, 10 figures; submitted to J. Phys: Condens. Matter for the
special issue 'Condensed Matter Analogues of Cosmology'; v2: considerably
reduced length, incorporation of experimental details into main text,
discussion improved, references added, version accepted for publicatio
The suppression of magnetism and the development of superconductivity within the collapsed tetragonal phase of Ca0.67Sr0.33Fe2As2 at high pressure
Structural and electronic characterization of (Ca0.67Sr0.33)Fe2As2 has been
performed as a func- tion of pressure up to 12 GPa using conventional and
designer diamond anvil cells. The compound (Ca0.67Sr0.33)Fe2As2 behaves
intermediate between its end members-CaFe2As2 and SrFe2As2- displaying a
suppression of magnetism and the onset of superconductivity. Like other members
of the AEFe2As2 family, (Ca0.67Sr0.33)Fe2As2 undergoes a pressure-induced
isostructural volume collapse, which we associate with the development of As-As
bonding across the mirror plane of the structure. This collapsed tetragonal
phase abruptly cuts off the magnetic state, giving rise to superconductivity
with a maximum Tc=22.2 K. The maximum Tc of the superconducting phase is not
strongly correlated with any structural parameter, but its proximity to the
abrupt suppression of magnetism as well as the volume collapse transition
suggests that magnetic interactions and structural inhomogeneity may play a
role in its development. The pressure-dependent evolution of the ordered states
and crystal structures in (Ca,Sr)Fe2As2 provides an avenue to understand the
generic behavior of the other members of the AEFe2As2 family.Comment: 9 pages, 9 figure
Can HERA See an Signal of a Virtual Leptoquark?
Virtual leptoquarks could be detected at HERA through some nonstandard
effects. Here we explore the possibility that virtual leptoquarks could be
discovered via scattering, assuming integrated luminosity of 200
pb and charm identification efficiency of 1%. We study the implications
of low energy data for the leptoquarks couplings and find that the most
relevant bound for the HERA cross sections comes from inclusive . This bound implies that the cross sections for
virtual leptoquarks are just too small for observation of the signal. With an
improvement by a factor of ~2 on the luminosity or on charm identification it
could be possible to see virtual leptoquarks with {\it maximum couplings} up to
~1.5 - 2 TeV. However, the prospects for discovering the virtual particles if
their couplings are somewhat below present bounds are very dim. We point out
that this cross section could be very large for leptoquarks lighter than HERA's
kinematical limit, and if such a leptoquark is discovered we recommend
searching for a possible signal. Our results may also serve as an
update on the maximum cross sections for leptoquark mediated
scattering.Comment: 15 Pages (LaTeX), including 4 postscript figures at the end of the
file. Feynman diagrams available by reques
Fractal Characterizations of MAX Statistical Distribution in Genetic Association Studies
Two non-integer parameters are defined for MAX statistics, which are maxima
of simpler test statistics. The first parameter, , is the
fractional number of tests, representing the equivalent numbers of independent
tests in MAX. If the tests are dependent, . The second
parameter is the fractional degrees of freedom of the chi-square
distribution that fits the MAX null distribution. These two
parameters, and , can be independently defined, and can be
non-integer even if is an integer. We illustrate these two parameters
using the example of MAX2 and MAX3 statistics in genetic case-control studies.
We speculate that is related to the amount of ambiguity of the model
inferred by the test. In the case-control genetic association, tests with low
(e.g. ) are able to provide definitive information about the disease
model, as versus tests with high (e.g. ) that are completely uncertain
about the disease model. Similar to Heisenberg's uncertain principle, the
ability to infer disease model and the ability to detect significant
association may not be simultaneously optimized, and seems to measure the
level of their balance
Pressure-induced superconductivity in the giant Rashba system BiTeI
At ambient pressure, BiTeI is the first material found to exhibit a giant
Rashba splitting of the bulk electronic bands. At low pressures, BiTeI
undergoes a transition from trivial insulator to topological insulator. At
still higher pressures, two structural transitions are known to occur. We have
carried out a series of electrical resistivity and AC magnetic susceptibility
measurements on BiTeI at pressure up to ~40 GPa in an effort to characterize
the properties of the high-pressure phases. A previous calculation found that
the high-pressure orthorhombic P4/nmm structure BiTeI is a metal. We find that
this structure is superconducting with Tc values as high as 6 K. AC magnetic
susceptibility measurements support the bulk nature of the superconductivity.
Using electronic structure and phonon calculations, we compute Tc and find that
our data is consistent with phonon-mediated superconductivity.Comment: 7 pages, 7 figure
The number of conjugacy classes in pattern groups is not a polynomial function
A famous open problem due to Graham Higman asks if the number of conjugacy classes in the group of n x n unipotent upper triangular matrices over the q-element field can be expressed as a polynomial function of q for every fixed n. We consider the generalization of the problem for pattern groups and prove that for some pattern groups of nilpotency class two the number of conjugacy classes is not a polynomial function of q
Isokinetic Peak Torque in Young Wrestlers
This is the publisher's version, also found at http://ehis.ebscohost.com/ehost/detail?vid=3&sid=34ab1967-2aea-457b-b261-e90e7b05e38c%40sessionmgr11&hid=2&bdata=JnNpdGU9ZWhvc3QtbGl2ZQ%3d%3d#db=s3h&AN=20752369The purpose of the present study was to examine age-related changes in
isokinetic leg flexion and extension peak torque (PT), PT/body weight (PT/
BW), and F*T/fat-free weight (PT/FFW) in young wrestlers. Male wrestlers (A^
= 108; age M ± SD = 11.3 + 1.5 years) volunteered to be measured for peak
torque at 30, 180, and 300° • s'. In addition, underwater weighing was performed
to determine body composition characteristics. The sample was divided
into six age groups (8.1-8.9, n = 10; 9.0-9.9, n= 11; 10.0-10.9, n = 25;
11.0-11.9, n = 22; 12.0-12.9, n = 28; 13.0-13.9, n= 12), and repeated measures
ANOVAs with Tukey post hoc comparisons showed increases across
age for PT, PT/BW, and PT/FFW. The results of this study indicated that there
were age-related increases in peak torque that could not be accounted for by
changes in BW or FFW. It is possible that either an increase in muscle mass
per unit of FFW, neural maturation, or both, contributes to the increase in
strength across age in young male athletes
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